A bipartisan group of senators formally unveiled an immigration reform framework that they hope the Senate could pass "in overwhelming and bipartisan fashion" by late spring or early summer.

Speaking at a press conference on Monday on Capitol Hill, five of the eight members of a bipartisan working group announced the contours of their agreement, which would shore up America's borders and provide an eventual path to citizenship for undocumented workers.

A bipartisan group of senators, led by Democrat Chuck Schumer and Republican John McCain, have reached agreement on a framework to overhaul the nation's immigration system.

"We still have a long way to go, but this bipartisan grouping is a major breakthrough," New York Sen. Charles Schumer, a Democratic member of the group of eight, said Monday afternoon.

Schumer, the No. 3 Democrat in the Senate, set an ambitious goal of translating the statement of principles released Sunday evening by the senators into legislation by March. He said the Senate would try to approve the legislation for consideration in the House by the end of spring, or early summer.

The major development involves the pathway to citizenship for undocumented workers that would be established under the Senate plan. Conservatives have resisted similar proposals -- even when they were proposed by President George W. Bush -- and labeled them as "amnesty" for individuals who entered the United States illegally.

Sen. John McCain, R-Ariz., said that Americans "have been too content for too long" to allow many undocumented workers to provide basic services "while not affording them any of the benefits that make our country so great."

Key Democrats and Republicans are joining forces to strengthen security and develop new rules for illegal immigrants who fill special needs. NBC's Kelly O'Donnell reports.

"It is not beneficial to this country to have these people here, hidden in the shadows," added McCain, whose own experience on the issue of immigration provides an instructive example of why immigration reform has been so elusive for Congress.

McCain had long been one of the most vocal advocates of a pathway to citizenship for undocumented workers, but tempered his opinions in recent years amid conservative scrutiny. As he was fighting off a conservative primary challenger in 2010, McCain appeared in a television ad saying it was time to "build the danged fence" -- a reference to the proposed fence along the U.S.-Mexico border, which is favored by a number of Republicans.

The senators' announcement on Monday comes a day before President Barack Obama was set to make a major policy address on Tuesday in Nevada on the topic of immigration. While Obama had not been expected to outline any formal legislation during his remarks, lawmakers from both parties will carefully parse the president's words for their impact on the immigration debate. Schumer said that he had spoken to the president about the Senate framework, and that the president was "delighted" by it.

Obama himself had vowed to achieve comprehensive immigration reform during his first term, but his efforts were stymied. That failure invited a degree of consternation from the Latino community during last year's presidential campaign, even though Obama had taken executive action to halt the deportation of individuals who were illegally brought to the United States as children.

(That order, made by Obama last summer, sought to effectively enact much of the DREAM Act, a piece of legislation that failed in the Senate as recently as 2010, when some Republicans who'd previously supported the law flipped, and voted against it.)

Indeed, the success of this push in the Senate may well hinge on Republicans' willingness to go along with a plan that gives undocumented immigrants a path to citizenship. Texas Rep. Lamar Smith, an influential House Republican, already labeled the Senate framework as "amnesty" in a statement on Monday.

House GOP leaders were otherwise mum on Monday toward the Senate proposal, though top Republicans have previously expressed a preference for tackling immigration in a piecemeal manner.

Florida Sen. Marco Rubio, a member of the eight-member group and a favorite of conservatives, has worked to gather conservative support for the proposal. He said at Monday's press conference that while no one is happy about the estimated 11 million immigrants living in the United States illegally, "We have an obligation and need to address the reality that we face."

The other factor weighing upon Republicans involves their poor performance among Hispanic voters -- a bloc that is growing in importance in a variety of key battleground states -- during last fall's election.

"The Republican Party is losing support of our Hispanic citizens," McCain said Monday in a nod toward a variable that could convince more GOP lawmakers to support this bipartisan proposal. But, McCain noted, "We're not going to get everybody onboard."

In the meanwhile, Senate Majority Leader Harry Reid, D-Nev., pledged to "do everything in [his] power as the majority leader to get a bill across the finish line."

"Nothing short of bipartisan success is acceptable to me," he said in remarks on the Senate floor preceding the group of eight's press conference.